There are two basic technologies presently used in telephony, digital and analog. For many years analog phones have been a standard communication device in households and businesses across the world. The analog phone operates by transmitting a continuous (analog) electronic representation of a person's voice signal across a communication network to another endpoint that is also connected to the network. Analog phones are connected to the phone company's office with a pair of copper wires, which supply power to the phone, and carry voice signals to/from the phone. Generally, power supplied by analog telephone lines is a more reliable source of power than typical power lines. This is because power lines utilize higher voltage and current than analog telephone lines do, and as a result power lines are much more interconnected than analog telephone lines. Because power lines are more interconnected than typical analog telephone lines, a power outage in one portion of the power grid may result in a power failure in another portion of the power grid.
Digital phones, examples of which include a Voice over IP (VoIP) phones and Digital Control Protocol (DCP) phones, on the other hand have been developed to transmit a digital representation of a person's voice signal across a communication network to another endpoint that is also connected to the network. Advantages offered by digital phones over analog phones include an increased signal processing speed and a reduced amount of noise present on the digital lines when compared to analog lines. Since there is less noise, digital phones are able to transmit data at much higher rates at much better quality levels than their analog counterparts.
However, many digital phones, particularly VoIP or IP phones, have the drawback that they may not continue to operate during a power failure. Some of the first models of IP phones required either a local power supply or were supplied power through the national power grid. In other words, the IP phones were just plugged into outlets of a wall (e.g., 120V, 60 Hz outlets in the United States or 230V, 50 Hz outlets in Australia and Europe). The downside to using phones that are connected to the national power grid is that they are susceptible to failure as the power grid fails. Since most power lines are exposed to the elements instead of being buried underground, the likelihood of power failures in parts of the national power grid is relatively high. More recently, however, Power over Ethernet (PoE) has been used to transmit electrical power, along with data, to a remote device over a standard twisted-pair cable in an Ethernet network. PoE may be used to power telephones, wireless Local Area Network (LAN) access points, webcams, Ethernet hubs, computers, and other appliances with direct current (DC) provided through the Ethernet cable where a separate power supply would be inconvenient and/or infeasible. However, in most PoE scenarios, DC power is supplied to an IP phone from the Ethernet switch connected to the phone. In another PoE scenario, power is supplied from devices located between the Ethernet switch and the device being powered. One downside to utilizing a DC power source is that the range of the power transmission is limited. Usually, if the power fails in the area of the IP phone(s), odds are the power has also failed at the source of the DC power. Uninterruptible Power Supplies (UPS) may be used as a backup in case the power fails, but in the event of a prolonged power failure, the UPS may run out of energy for supplying power to the phone(s). Furthermore, IP phones require relatively more power than do their analog and digital non-IP counterparts. Thus, even though IP phones offer many benefits when compared to analog and digital non-IP phones, they still do not have the advantage of being powered by the phone company. IP phones suffer from a dependence upon two services, whereas analog phones are reliant only on one service. IP phones are susceptible to communication failures if either one of the communication network or the power supply fails. Thus, IP phones have two points of failure, whereas analog phones only have a single point of failure because the same line provides both the power and the communications to the analog phone.
One particular concern is that during a power failure, individuals may need to make an emergency call. In the event that the only type of phone they have available is an IP phone, and the power to the IP phone has been interrupted, then it may not be possible to make such an emergency call. Also, if the power fails, the user will most likely require a separate analog phone if they wish to make any calls. Their backup analog phones may not easily be located during a power failure due to decreased lighting. In some emergencies, such as those requiring Cardiac Pulmonary Resuscitation (CPR) to be administered, there may be no time or opportunity to search for and/or use a designated analog phone. Generally, users do not keep an IP phone and an analog phone available for use side-by-side because doing so would-take up-valuable desk space. In fact, most phone users purchase an IP phone to replace their analog phone, but as discussed above, the IP phone has drawbacks that traditional analog phones do not. The dependence of IP phones upon power supplies that are not as reliable as power supplies of analog phones is a major drawback of current IP phones.
There have been some attempts to create a hybrid-IP phone such that the IP phone can be used during network outages. Specifically, NEC™ has developed an IP phone that is powered by PoE and has optional adapters that can expand the capability of the phone. Adapters can be added to the IP phone such that the phone has a backup PSTN circuit that provides incoming and outgoing call capabilities. However, these IP phones typically use two ports, one for connecting to a circuit-switched network and the other for connecting to the packet-switched network. The additional ports and cables required to provide the switching feature for most of these IP phones are cumbersome in that the additional wires clutter a desktop. Furthermore, these additional ports and cables must be installed and connected through the walls, tracked, and connected to a router. The additional ports and cables result in additional costs and points of potential failure to the phone.